Connected: An Internet Encyclopedia
RFC 1144 - 1 Introduction

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### 1 Introduction

As increasingly powerful computers find their way into people's homes, there is growing interest in extending Internet connectivity to those computers. Unfortunately, this extension exposes some complex problems in link-level framing, address assignment, routing, authentication and performance. As of this writing there is active work in all these areas. This memo describes a method that has been used to improve TCP/IP performance over low speed (300 to 19,200 bps) serial links.

The compression proposed here is similar in spirit to the Thinwire-II protocol described in [5]. However, this protocol compresses more effectively (the average compressed header is 3 bytes compared to 13 in Thinwire-II) and is both efficient and simple to implement (the Unix implementation is 250 lines of C and requires, on the average, 90us (170 instructions) for a 20MHz MC68020 to compress or decompress a packet).

This compression is specific to TCP/IP datagrams./2/ The author investigated compressing UDP/IP datagrams but found that they were too infrequent to be worth the bother and either there was insufficient datagram-to-datagram coherence for good compression (e.g., name server queries) or the higher level protocol headers overwhelmed the cost of the UDP/IP header (e.g., Sun's RPC/NFS). Separately compressing the IP and the TCP portions of the datagram was also investigated but rejected since it increased the average compressed header size by 50% and doubled the compression and decompression code size.

2. | The tie to TCP is deeper than might be obvious. In addition to the compression `knowing' the format of TCP and IP headers, certain features of TCP have been used to simplify the compression protocol. In particular, TCP's reliable delivery and the byte-stream conversation model have been used to eliminate the need for any kind of error correction dialog in the protocol (see sec. 4).

Next: 2 The problem

Connected: An Internet Encyclopedia
RFC 1144 - 1 Introduction